Your boiler thinks a flame is burning even though it shouldn't be, causing the system to shut down for safety.

False flame lockout

What causes this fault?

This fault occurs when the boiler's internal sensors detect a flame after the burner has been told to switch off, or before it has even started. It is usually caused by a faulty sensing probe sending an incorrect signal to the main control board, or a leak inside the unit that has allowed moisture to interfere with the electrical components.